Pressure switch



Nov. 3, 1942. EH; HOPKINS 2,300,897

PRESSURE SWITCH Filed March 17. 1942 4 1; Ash/6 1 wmwmi Patented Nov. 3,, 1942 PRESSURE SWITCH Frank H. Hopkins, Fairfield, Conn, assignor to Manning, Maxwell & Moore, Incorporated, New York, N. Y., a corporation of New Jersey Application March 17, 1942, Serial No. 435,059

. 7 Claims.

This invention relates to an improvement in pressure controlled instruments, and more particularly in an instrument of the type shown in my copending application Serial No. 423,942, filed December 22, 1941, upon which the present invention is a further development.

The primary object of this invention resides in the provision in a pressure-controlled instrument comprising a snap switch and a pressurecontrolled actuator therefor, of means by which the switch contact point, and the range between the opening and closing of the switch may be independently adjusted.

A further object of this invention resides in the provision of a separate terminal plate which is removably secured to the switch block and by means of which the necessity for splicing the wires of the circuit within the switch housing is eliminated.

These and other objects of the invention will appear from a consideration of the following description of the invention and of the accompanying drawing which illustrates the invention and in which:

Fig. l is a side elevation of an instrument embodying the invention, the housing thereof being broken away;

Fig. 2 is an end elevation of the instrument shown in Fig. 1 with parts broken away and the Bourdon tube omitted;

Fig. 3 is a bottom plan view with parts broken away;

Figs. 4 and 5 are enlarged cross-sectional views of the switch block taken along the section lines 4-4 and 5-5, respectively, of Fig. 6;

Fig. 6 is a side elevation of an instrument embodying another form of the invention, the housing being omitted;

Fig. 7 is a diagrammatic view illustrating a motor circuit in which the instrument is an element; and

Fig. 8 is a diagrammatic view illustrating the essential elements of the switch.

The invention is shown in the drawing as ap plied to the operation of a switch H] of the snap operating type of the kind known as a Mu switch made by the Mu Switch Corporation, of Boston, Massachusetts. It will be understood, however, that the invention is not limited thereto, and that it is applicable to the operation of other switches of the same general type. The switch l0 includes a hollow block or housing le of insulating material having a bushing in its top or cover providing a guide for a vertically slidable pin l I a spring arm I2 is fixed at one end to the top or cover of the switch block with its free end overlying the pin H. The specific internal construction of the switch forms no part of the present invention, although its essential features are diagrammatically illustrated in Fig. 8, and will hereinafter be referred to more fully.

The switch I!) is mounted in a housing or casing which also contains a Bourdon tube It mounted at its stationary end in a socket ll in a post l8 mounted within the housing l5. The free end of the tube carries a finger l9 so positioned with respect to the switch 10 and more particularly the free end of the arm [2 that upon the contraction of the tube in response to a reduction in pressure, the finger 19 engages the arm I 2, causing the latter to depress the pin II and thus close or open the circuit of which the switch is an element.

One feature of this invention resides in the adjustment of the position of the switch l0 relative to the finger IQ of the Bourdon tube [6 whereby the length of travel of the finger 19 before the switch is closed by the movement of the tube is varied as desired. Thus, the amount of reduction in pressure permissible before the circuit is closed can be set at any predetermined point.

In order to carry out this purpose, the switch I0 is so mounted that it can be rotated within the housing about a fixed center. As shown, particularly in Figs. 2 and 3, the post I8 is rigidly secured to the back wall 20 of the housing [5 by screws 2l-spacers 22 being inserted to hold the post out of contact with the wall 20. The switch H! is rigidly mounted by screws 23 (leg. 3) upon a backing plate 24 which in turn is mounted upon an upward extension l8 of the post [8 by a single stud 25 (Fig. 2), preferably at or closely adjacent to the center of the wall 20. The stud 25 projects through the part H3 and has a head 26 which enters a keyhole slot in a bowed spring 21 (Fig. 2) between the spacers 22. Thus, the switch is rotatable and is yieldably held against the part w Preferably, as here shown, the upper part [8 of the post I8 which supports the switch is cut away to make the instrument more compact.

Loosely pivoted near the left-hand end of the backing plate 24 (as viewed in Fig. 1), adjacent to the pin II, is a bracket 38 having a threaded hole therein which receives a screw-threaded bolt 3| mounted to rotate in a bracket 32 fixed to one wall of the housing [5. The head 33 of the bolt is provided with a plurality of slots 34 by which the bolt can be turned. An expansion spring surrounds the bolt 3| and bears at its ends against the brackets 30 and 32. Thus, by turning the bolt 3|, the switch Hi can be rocked about the stud 25 as a center and the normal distance between the bar I2 and the finger is varied.

A second feature of this invention resides in the provision of means whereby not only the pressure at which the switch is closed is varied but also the differential range between the closing and opening of the circuit can be adjusted. This range varies with the distance between the pin H and the point on the arm l2 which is engaged by the finger of the Bourdon tube It. The travel of the free end of the arm I2 in one direction closes the switch and conversely the reverse movement of the arm l2 permits the switch to open after it has been closed. The distance traveled by the pin I to close and open the switch is uniform. However, the length of travel of the tip I9 of the tube necessary to induce switch closing movement of the pin increases as the distance from the pin H to the point on the arm l2 engaged by the tube-tip or finger l9 increases.

Fig. 6 illustrates one way of varying this distance. Fixed to the finger IQ of the Bourdon tube I6 is a nut 4| which has threaded engagement with a screw 40, the finger is having an opening (not shown) in registry with the hole in the nut. The nut 4| may be soldered or otherwise fixed on the finger l9. The head 32 of the screw contacts the arm It as the tube I6 contracts in response to decreasing pressure, and as the contraction continues, the pin H is depressed to close the circuit. By rotating the screw 4|] in the nut 4|, the distance between the pin II and the point on the arm l2 at which the head 42 engages it can be adjusted as desired.

A third feature of this invention resides in th provision of means whereby the instrument can be quickly, easily and securely made an 81!.- ment of a typical electrical circuit such, for example, as that shown diagrammaticall in Fig. 7 of the drawing. Mounted upon one side face of the switch I0 is a connector unit having a base 5| of dielectric material and separators 52, 53, 54, and 55 also of dielectric material which project forwardly from the base 5|. Preferably the separators are integral with the base as shown in the drawing, but it will be understood that this is not essential and that the separators may be formed independently and mounted on the base. The end separators 52 and 56 include wings 5'1 and '53 which project rearwardly from the back wall of the base, the length of the back wall being such that the wings 51 and 58 extend over the end walls of the switch, as shown in Fig. 3. The separators define pockets in which bus bars are removably mounted by screws 60 (see Figs. 4 and 5). The two bus bars 6| and 62 which are located in the end pockets defined by the separators 52, 53, 55, 55, respectively, are bent to right angular form, and when the unit is mounted on the switch, these bars extend from the upper face of the switch along the side and bottom walls thereof (Figs. 3, 4 and 5). Mounted in the intermediate pockets defined by the separators 53, 54 and '55 is a bus bar 63. The bar 63 is C-shaped and the upper end of the separator 54 is omitted so that the bar 63 fills both the pockets as shown in Figs. 1 and 6. In threaded engagement with the bus bars are set screws 64, 6t, 64 64 respectively, which, as will appear below, constitute binding posts to which the ends of various conductor leads are secured. The base 5| is so shaped that the inner ends of the screws E4 do not engage it.

The assembly of the unit 50 upon a switch will now be described with particular reference to the Mu switch It. This switch includes a spring strip 65 with which the pin is, at all times, in contact (see Fig. 4). That end of the strip 65 which is adjacent to the pin is fixed to a pair of tubular, internally threaded metal posts 66, by means of screws 61. Also carried by the posts 66 is a plate 63 having a raised fulcrum portion $9 on Which the strip 65 rests. The other end of the strip 65 is unsupported and enclosed by a clip 13 (Fig. 5) rigidly secured thereto. The clip 10 is located between plates H and i2 carried by tubular internally threaded metal posts 13 and M, respectively, to which they are secured by screws 15. The clip 10 normally rests upon the plate H and out of contact with the plate 12. The pin rests on the strip 35 between the posts 66 and the raised portion 69 so that when the pin II is depressed, the strip 65 is flexed and the clip 10 is suddenly snapped up into contact with the plate 12. The tubular posts B6, 13 and M are electrically joined to the strip 65 and to the plates H and 12, respectively, and extend through holes in the body of the switch but terminate short of the bottom face of the switch.

When the unit 59 is assembled with the switch it, the wings 51 and 58 bear against the end walls of the switch and the bars 6| and 52 extend below and out of contact with the posts 66, and 13, M, respectively, as shown in Figs. 3, 4 and 5. Screws 1B pass through the bar 6| into the posts 66 and a screw 11 passes through the bar 62 into the post 14 and secures the unit in position. Thus, the bar 6| is electrically connected at all times with the strip 65 and the bar 62 is electrically connected at all times with the bar 12. If it be desired to arrange the switch so that it will close when the clip 10 contacts the bar instead of the bar 12, then the screw 11 may be shifted to engage the post 13 instead of the post M.

The circuit shown in Fig. 7 comprises a motor 89, iced lines 8|, 82 and the switch It]. A lead wire 83 connects the live line 8| to the binding post 64 as bus bar BI and a second lead wire 84 extends from one side of the motor to the binding post 64 on bus bar 62, while the other side of the motor is connected to the grounded line 82 by lead wires 85 and 85 connected to binding posts M and 64 on the bus bar 63. The lead wires are quickly, easily and securely attached to the bus bars by means of the screws 64, and the switch is thereby made an element of both sides of the circuit. As shown in Fig. 1, the lead wires 83, 85 enter the housing l5 through a conduit 81 and the lead wires 84, 88 enter the housing through a second conduit 83. While such an arrangement has been found satisfactory, it will be understood that other arrangements may be made depending upon various conditions, as for example the location of the instrument and its relation to the motor.

In considering the operation of the instrument, it will be assumed that it forms a part of the motor control circuit illustrated in Fig. 7, and that the motor is arranged to operate a pump for automatically establishing certain desirable pressure conditions, for example, in a water supply system.

It will be understood that musing a switch of the kind herein described, the actuating pin II must be moved downwardly to a definite predetermined amount in order to flex the plate 65 sufficiently to snap the switch closed or to permit the plate to flex upwardly to cause the switch to open. Considering the arm I2 as a lever pivoted at one end, it is evident that this lever always contacts the pin II at the same distance from the fulcrum end of the lever and that this point of contact must always travel thesame distance in depressing the pin I I sufficiently to snap the switch shut. On the other hand, points along the arm I2 beyond the pin II move different amounts (proportionate to their distances from the fulcrum of the lever) when the arm is rocked through the necessary angle to depress the pin II in closing the switch. Thus, for instance, if the finger I9 first contacts the arm I2 at a given distance beyond pin I I when the pressure in the system has dropped to twenty pounds, then the finger I9 may be required to move farther until the pressure has dropped, for example, to ten pounds, before the switch actually snaps closed. Conversely, before the switch can open and thus stop the pump motor, the finger I9 must be moved upwardly to a point corresponding to a pressure of twenty pounds in the Bourdon tube. This pressure differential represents the period during which the pump will be operated.

Obviously, if the finger I9 had been caused first to engage the arm 12 at a point nearer the pin II than in the example just given, and assuming that the finger I9 engaged the arm I2 at the same initial pressure, that is to say twenty pounds, then a lesser continued downward movement of the finger I9 would be requisite to force the pin I I downwardly, thereby to snap the switch than in the previous instance, and thus the switch might actually snap closed at a pressure of fifteen pounds instead of ten pounds. Conversely, as the pump is operated and the pressure is built up, there will be a shorter period of operation of the pump before the switch is again snapped open and the motor stopped. Thus, the pressure differential or gap between the starting and stopping of the motor may be controlled by varying the effective point along the arm I2 at which the finger I9 operatively engages the arm. This variation in the contact point may be accomplished in various ways, as for example by bending the finger I9 so that its tip approaches or recedes from the pin II longitudinally of the arm I2 or,

as illustrated in Fig. 6, the contact may be made between the adjustable element 42 carried by the finger I9 and the arm I2, such adjustment being made merely by rotating the part 42.

On the other hand, the pressure at which the finger S9 or the contact element carried thereby first engages the arm I2 may readily be adjusted by turning the screw SI, thereby rocking the entire switch about the pivot pin 25 and thus causing the arm I2 to approach or recede from the finger I9 or the contact element carried thereby. Thus, the pressure at which the instrument is set to start the motor into operation may readily be varied to a very accurate degree.

The Mu type of snap switch which is here 11- lustrated is of the single pole variety, that is, it breaks one side of the motor circuit only. Gus-- tomarily the ground wire of the circuit is not attached to the snap switch at all but merely passes through the housing in which the snap switch 63, thus permitting ready connection of the ground leads without necessitating splicing.

As above suggested, the snap switch itself is of standard type and made in accordance with standard practice so that the closing contact can be made either at the top side or the bottom side of the movable end of the switch spring. As here illustrated, and as above suggested, provision is made for this alternative arrangement by shifting the screw "I? from the post I4 to the post I3, if desired.

While certain embodiments of the invention have been described and their structure and func tion set forth in detail, it will be understood that the invention is not limited thereto, and that other embodiments of the invention may be made without departing from the spirit and scope thereof as set forth in the following claims.

I claim:

1. An instrument of the class described comprising a housing, a Bourdon tube, and an electrical switch, including a movable actuator, mounted within said housing, and means for transmitting movement from the tube to the actuator, said transmission means including a contact element supported by the tip of the tube, a support within the housing upon which the switch is mounted, pivot means for the switch support providing a horizontal axis about which the support may swing thereby to vary the initial position of the actuator relatively to the contact element, and means carried by said housing for rotating said switch and adjusting the distance between the tip and the movable actuator, such rotating means comprising a bracket loosely pivoted to the switch support at a substantial distance from the pivotal axis of the latter, said bracket having a threaded hole therein, a second bracket fixedly mounted upon said housing, and a screwthreaded bolt rotatably supported by said fixedly mounted bracket and engaging the threaded hole in the first bracket.

2. An instrument of the class described comprising a housing, a Bourdon tube, and an elec trical switch, including a movable actuator, mounted within said housing, and means for transmitting movement from the tube to the actuator, said transmission means including a contact element supported by the tip of the tube, means supporting the switch for pivotal movement thereby to vary the initial position of the actuator relatively to the contact element, a switch-supporting member, pivot means for the switch-supporting member defining a horizontal axis about which the supporting member may be swung for rotating said switch and thereby adjusting the distance between the tip and the movable actuator, a bracket loosely pivoted to said supporting member, said bracket having a threaded hole therein, a second bracket fixedly mounted upon said housing, a screw-threaded bolt rotatably supported by said fixedly mounted bracket and in threaded engagement with the hole in said loosely pivoted bracket, and a coiled compression spring surrounding the bolt and bearing at its ends against said brackets,

3. An instrument of the class described comprising a housing, a Bourdon tube and a snap switch mounted therein, said switch including a depressible pin and an elongate actuating arm resting thereon, which arm, in response to pressure applied, depresses said pin and closes said switch, a finger carried by the free end of said tube, a screw in threaded engagement with said finger, the axis of the screw being substantially parallel to said actuating arm, the screw having a head which is brought into contact with said arm upon contraction of said tube, said screw being adjustable relative to said finger to vary the point longitudinally of the arm at which contact of the head contacts the arm.

4. In an instrument of the class described designed for use in an electrical circuit comprising a live line and a grounded line, a snap switch including an insulating block having one end of a spring arm fixed thereto and a normally fixed contact with which the free end of the arm may be engaged, and a connector unit removably attached to said insulating block, said connector unit having a pair of independent relatively insulated binding posts electrically connected respectively to the spring arm and to the contact, said binding posts being designed to receive terminals of the live line of the circuit, said unit also comprising a pair of electrically connected binding posts each designed to receive one terminal respectively of the grounded line of the circuit.

5. In an instrument of the class described designed for use in an electrical circuit comprising a live line and a grounded line, a snap switch including an insulating block having one end of a spring arm fixed thereto and a normally fixed contact with which the free end of the arm may be engaged, a connector unit comprising three relatively insulated bus bars, two of said bars being provided each with one binding post and the third bus bar being provided with two binding posts, the single-post bars having openings for attaching screws by means of which the unit may be secured to the insulating block of the switch, said screws also constituting means for electrically connecting said bus bars to the spring arm and to said contact respectively, the single post bars being designed respectively to receive the terminals of the live line of the circuit, and the two-post bar being designed to receive two terminals of the grounded line of the circuit.

6. In an instrument of the class described designed for use in an electrical circuit comprising a live line and a grounded line, a snap switch including an insulating block having one end of a spring arm fixed thereto, a pair of normally fixed contacts with one of which the free end of the arm normally engages and with the other of which it may be caused to engage at times, and a connector unit comprising three bus bars, two of said bars being provided each with one binding post and the third bar being provided with two binding posts, the single-post bars having openings for the reception of attaching screws by means of which the unit may be secured to the insulating switch block, the attaching screw for one of said single-post bars being normally electrically connected with the spring arm, the attaching screw for the other of said single-post bus bars being shiftable at will thereby to provide electrical connection between the bar and either of said contacts alternatively, the binding posts of said single-post bars being designed to receive the terminals of the live line of the circuit, and the two posts of the two-post bar being designed to receive the terminals of the grounded line of the circuit.

7. In an instrument of the class described including a switch having spaced contacts and means for electrically connecting said contacts to close said switch, a connector unit removably mounted upon said switch, said unit comprising a base of dielectric material, separators of dielectric material carried by said base and defining pockets therewith, three relatively insulated bus bars mounted in said pockets, means for electrically connecting two of said bus bars, respectively, with the respective contacts of the switch, binding posts for connecting said latter bus bars respectively to the terminals of the live side of a circuit, and a pair of electrically connected binding posts on the third bus bar designed to receive the terminals of the grounded side of the circuit.

FRANK H. HOPIUNS. 

